The objectives of this project are: 1) To isolate and amplify genes coding for phenylalanine tRNA from Friend virus transformed mouse erythroleukemia cells. 2) To determine the nucleotide sequences of transcribed and non transcribed DNA loci in mouse phe tRNA genes. 3) To isolate phe tRNA precursors, including the primary transcription products of phe tRNA genes. 4) To determine the heterogeneity of DNA loci (intervening and flanking regions) associated with the reiterated phe tRNA coding sequence. 5) To determine the function of non-coding sequences within phe tRNA genes. 6) To determine whether individual genes coding for phe tRNA are expressed differentially during the in vitro differentiation of mouse Friend cells. These will be accomplished by: 1) Inserting Friend cell DNA segments containing phe tRNA genes into recombinant plasmids and isolating bacterial clones harboring them. 2) Sequencing recombinant plasmids containing phe tRNA genes. 3) Isolating tRNA precursors from pulse-labelled Friend cells using plasmids as affinity reagents. 4) Comparing the restriction maps and sequences of a number of independently derived clones coding for phe tRNA. 5) Examining the transcription of cloned DNAs and their histone complexes in vitro by eucaryotic RNA polymerases. 6) Determining the number of phe tRNA genes present in a chromatin conformation sensitive to DNase I in non-induced and induced (differentiated) FL cells.